International patent application WO 01/30407 A1 describes a method for the production of hydrogels for use as wound dressings with which burns or other skin injuries can be treated. Within the scope of the method, an aqueous solution of polyvinyl alcohol, agar-agar and at least another natural polymer is prepared. This solution is filled into disposable plastic containers at 70° C. to 80° C. and sealed. After having cooled off to room temperature, the samples that had been filled into the disposable plastic containers are irradiated and thus sterilized.
International patent application WO 2005/103097 A1 describes hydrogels that have at least one polyvinyl alcohol star polymer. Here, the hydrogels are produced by repeatedly freezing and thawing an aqueous solution containing at least one polyvinyl alcohol star polymer and optionally additional components. Moreover, such hydrogels can be produced through the action of ionizing radiation of an aqueous solution containing at least one polyvinyl alcohol star polymer or by reacting a polyvinyl alcohol star polymer in an aqueous solution with cross-linking reagents.
A drawback of the currently known methods for the production of hydrogels, especially for treating wounds, is the laborious production method and the problematic further processing of the hydrogels as well as, if applicable, the occurrence of chemical impurities in the hydrogels that have been cross-linked, for instance, by means of a chemical reaction. Moreover, hydrogel films, in contrast to fibers and fibrous structures, have a smaller surface area, as a result of which they have less absorption capacity for water or aqueous solutions. Especially when polyvinyl alcohol is used as the raw material for hydrogels, care must be taken to ensure that the polyvinyl alcohol has a high degree of cross-linking since otherwise, no hydrogels are formed but instead, solutions of the polyvinyl alcohol in the liquid medium. Consequently, a high stability of the polyvinyl alcohol vis-à-vis water or aqueous solutions is desirable. Moreover, it is precisely polyvinyl alcohol and polyvinyl alcohol copolymers that stand out for their high biocompatibility and biotolerability, so that there is a rising demand for further variants of hydrogels or hydrogelling materials containing polyvinyl alcohol and/or polyvinyl alcohol copolymers that can also be produced cost-effectively and easily, while allowing unproblematic further processing.
J. Mater. Sci. (2010) 45:2456-2465 describes a method for the production of nanofibers and fibrous structures made of polyvinyl alcohol by means of electrospinning, in which the fibers or fibrous structures are stabilized vis-à-vis aqueous solutions by means of a temperature treatment. A drawback of fibrous structures made of nanofibers is that, due to their fiber diameter, which is between 244 nm and 270 nm, they exhibit a very low strength and maximum breaking elongation as well as only a low absorption capacity. Furthermore, the described fibers are stabilized vis-à-vis aqueous solutions so that they have no gelling properties, do not swell in aqueous solutions and are not suitable to trap water in the fiber (lack of retention capacity).
Wound dressings made of hydrogelling fibers, for example, of carboxymethyl cellulose or modified cellulose, are fundamentally known. However, they form a very soft hydrogel with a low maximum breaking force and maximum breaking elongation upon contact with the wound fluid. The drawback here is that they are difficult to remove in one piece from the wound or from the wound cavity. Thus, it can happen that residues of the wound dressing are left behind in the wound, and these then have to be removed by means of laborious cleaning of the wound. This takes more time for the hospital personnel and thus also involves more costs. Moreover, the would can be damaged or injured again by the cleaning procedure.
Fibers made of polyvinyl alcohol are commercially available in various types and they include polyvinyl alcohol having different levels of water solubility. Water-insoluble types of polyvinyl alcohol are, for example, the so-called high-strength polyvinyl alcohol fibers having a particularly high maximum breaking force in the dry state. Commercially available water-soluble fibers made of polyvinyl alcohol can be obtained with a temperature-dependent water solubility, for example, a water solubility above a temperature of 90° C., 70° C., 60° C., 40° C. or 20° C. Commercially available fibers made of polyvinyl alcohol can vary in terms of their water solubility, but they have no hydrogelling properties and thus display no retention capacity for water either.